Introduction to tropical meteorology and deep convection

1. Introduction to tropical meteorology and deep convection Roger K. Smith University of Munich

2. Topics • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

3. INDO IR 01010510

4. GMS IR 01022621

5. GOES IR 00112909

6. Principal land and ocean areas between 40°S and 40°N. The shaded areas show tropical highlands (over 1000 m). From Nieuwolt (1977)

7. How does one define the tropics? Tropic of Cancer 23.5oN Maritime continent Tropic of Capricorn 23.5os

8. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

9. energy gain Radiative heat balance + energy loss 300 200 F (W m-2) - - Absorbed solar flux Emitted infrared flux 100 0 90 50 30 10 0 10 30 50 90 South Latitude North Zonally averaged components of the absorbed solar flux and emitted thermal infrared flux at the top of the atmosphere. (after Vonder Haar and Suomi, 1971, with modifications)

10. 2000 Mean annual precipitation 1500 mm 1000 500 0 90 60 40 30 20 10 0 10 20 30 40 60 90 North Latitude South Mean annual precipitation as a function of latitude. (after Sellers, 1965)

11. mean meridional circulation Hadley circulation  The mean meridional circulation and main surface wind regimes. after Defant, 1958

12. ITCZ

13. ITCZ

14. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

15. Field Experiments in the Tropics 1969 - 1979 • Bermuda Oceanographic and Meteorological EXperiment(BOMEX) 1969 • Holland & Rasmusson, (1973), MWR, 101, 44-55. • Global Atmospheric Research Programme (GARP) Atlantic Tropical Experiment(GATE) July 1974 • GARP: Fleming et al., (1979), BAMS, 60, 649-659. • GATE: Kuettner et al. (1974) BAMS, 55, 711-744. • The MONsoon EXperiment (WMONEX December 1978, SMONEX May – August, 1979) • WMONEX: Greenfield & Krishnamurti (1979), BAMS, 60, 649-659.SMONEX: Fein & Kuettner (1980) BAMS, 61, 461-474.

16. Field Experiments in the Tropics 1987 - • Australian Monsoon EXperiment & Equatorial Mesoscale EXperiment(AMEX, EMEX) January – February 1987 • AMEX Holland et al. (1986), BAMS, 67, 1466-1486. • EMEX Webster & Houze (1991), BAMS, 72, 1481-1505. • Tropical Oceans Global Atmosphere Couple Ocean Atmosphere Response Experiment(TOGA COARE) November 1992 – February 1993 • Webster & Lucas (1992), BAMS, 73, 1377-1416.

17. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

18. 200 mb JJA 850 mb

19. 200 mb DJF 850 mb

20. Velocity potential We can separate the three-dimensional velocity field into a rotational part and a divergent part (see e.g. Holton, 1972, Appendix C.) rotational nondivergent irrotational divergent

21. Upper tropospheric (200 mb) mean seasonal velocity potential indicating the divergent part of the mean seasonal wind which is proportional to . (Adapted from Krishnamurti et al., 1973).

22. month OLR < 225 W m-2 From Lau & Chan, 1983

24. Walker circulation

25. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

26. July Monsoons

27. SE Asian Monsoon

28. January

29. Australasian Monsoon

30. South America: January climatology 850 mb wind 200 mb wind

31. An example of monsoon variability West coast of India 1963 1971 (From Webster, 1983)

32. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

33. Time-longitude section of vis imagery - latitude band 10 -15 N 01/06 June 0107 July 0108 August time From Wallace, 1970

34. Winter MONEX Fig. 1.23 A B GMS – IR 25 Dec 1978 C MSLP 25 Dec 1978 From Webster, 1983

35. Winter MONEX Fig. 1.24 A 250 mb 25 Dec 1978 B C shaded horizontal wind divergence A 850 mb 25 Dec 1978 C B From Webster, 1983

36. The variation of surface pressure at Darwin for the period 23 - 28 Dec. 1978.

37. Easterly waves over Africa WV Imagery 17 June 1997 00Z

38. Tropical cyclones Super typhoon Wynnie 11 Aug 1997 TC tracks (1979-1988)

39. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

40. Moist Convection Trade Cumuli

41. The tropical troposphere z km 15 -73oC -121oC observed -150oC +150oC 77oC 29oC q observed Conclusion: Deep tropical circulations cannot be dry adiabatic

42. The role of diabatic processes z km 15 Latent heat release opposes adiabatic cooling Radiative cooling opposes adiabatic warming Fast ascent Slow descent ITCZ subtropical high Conclusion: Deep convection occupies a small fractional area

44. Radar reflectivity contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa). Horizontal cross-section at low levels (0.5 – 1.5 km). Successive locations of radar reflectivity contours in a tropical squall line.From Chang et al. (1987)

45. Radar reflectivity contours (dBZ) of a tropical squall line observed during COPT81 (Ivory Coast, West Africa). Vertical cross-section along the axis of propagation.

46. Types of convection

48. Next topic • A satpix tour of the tropics • The zonal mean circulation (Hadley circulation), Inter-Tropical Convergence Zone (ITCZ) • Field experiments • Macroscale circulations, The Walker circulation, Monsoons • Synoptic scale weather systems, tropical waves • Moist convection and convective systems • The Madden-Julian Oscillation, Westerly wind bursts • Concluding remarks

49. Madden-Julian Oscillation From JAS, Sept. 1972

50. Madden-Julian OscillationMJO From Webster 1987